The development of TMDLs for estuarine ecosystems like the Delaware River Estuary for classes of pollutants such as PCBs from multiple source categories requires innovative approaches. The Delaware Estuary was listed as impaired under Section 303(d) of the Clean Water Act by three bordering
states (DE, NJ, and PA) due to the levels of PCBs in the tissues of resident and anadromous fish species. Court mandates and administrative agreements between the U.S. EPA and state agencies required development of the TMDLs by December 2003. Several factors complicated the TMDL process for
this shared water including establishing the applicable water quality criteria (existing or new human health criteria, wildlife criteria); the lack of knowledge of the important hydrological, sedimentary and fate processes; the lack of data on ambient PCB concentrations and source loading;
and the need to develop a water quality model for PCBs. The scope and complexity of the overall project also lead to an agreement between the U.S. EPA, DRBC and state agencies to develop the TMDLs in two stages. Guided by an expert panel of scientists experienced in the assessment and modeling
of PCBs, initial efforts focused on 1) revising and expanding a current hydrodynamic model of the estuary; 2) establishing and calibrating a water quality model for one PCB homolog, pentachlorobiphenyls; 3) expansion of a network of air monitoring stations to assess the relative impacts of
regional and local sources of PCBs; 4) mapping of estuarine sediments and geophysical studies of important sediment processes; and 5) extensive picogram level congener data on ambient water, sediments and PCB sources including NPDES discharges, tributaries and air deposition. The first
stage was completed in December 2003, and all of the required TMDL elements were addressed in order to meet the court-ordered and administrative dates. Requirements for NPDES point sources in Stage 1 included additional monitoring using low level analytical methods for PCB congeners, and waste
minimization programs. Subsequent refinement of the TMDLs in the second stage, including the use of revised water quality criteria, and wasteload and load allocations that can be used to establish numeric and non-numeric permit limitations, is targeted for completion in two years. This staged
approach allowed the formulation of key findings that will guide further studies, and the identification of significant sources that can be targeted for additional characterization and source reduction while further development and refinement of PCB homolog models continue. Such staging of
the development of TMDLs for classes of pollutants with multiple sources in complex water bodies is strongly recommended.
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